You will need to access Course Settings to activate the course for students. Look in the upper-right part of the screen for the little gear icon next to ‘Turn editing on:’
When you click the little downward-facing triangle, the first choice is “Edit settings”:
Click on that, and then scroll down until you see “Course visibility.” It will be set to “Hide,” change it to “Show”:
Then, at the bottom of the page, click Save—and the course will be visible to students.